1. Technical Field
The invention is generally related to power amplifiers and, more particularly, is related to controlling bias current of a power amplifier.
2. Related Art
With the increasing power efficiency demands from users of mobile communication devices, such as cell phones and the like, mobile communication device manufacturers are continually searching for ways to improve power consumption efficiency within the mobile communication device, thereby increasing the useful operating period that a mobile communication device gets from a single charge of the power source, such as, but not limited to, a battery or fuel cell. During a normal voice conversation by a person using the mobile communication device, the transmitting function consumes a very large amount of available power. As such, energy conservation in transmitters is of paramount importance.
Conventional mobile communication devices typically consume large amounts of power as a voice signal is converted into a communication signal and amplified to a power level necessary for transmission from the mobile communication device to a base station. Within the communication industry, significant efforts continue to attempt to minimize power consumption. Therefore, there is an ongoing need to continue to reduce energy consumption in mobile communication devices.
The invention provides for dynamically biasing a plurality of amplifiers residing in a power amplifier. One embodiment employs at least one dynamic bias controller. Based upon the amplitude of a communication signal, such as a radio frequency (RF) signal, the dynamic bias controller deactivates (turns off) selected amplifiers (remove bias) when the communication device is to transmit a low power communication signal, and activates (turns on) the selected amplifiers (apply bias) when the communication device is to transmit a higher power communication signal. A plurality of dynamic bias controllers may control a plurality of amplifiers such that a plurality of communication signal strengths can be realized.
In the one embodiment, the dynamic bias controller may employ an attenuator that attenuates the detected communication signal. Those portions of the detected communication signal that are at least equal to the predetermined amplitude that are not attenuated, are rectified by a rectifying circuit. A low pass filter filters out AC components resulting in a base band signal that actuates a transistor residing in a switch. When the transistor is activated (turned on), an emitter follower transistor generates a control signal that activates a selected power amplifier.
Another embodiment further incorporates a prematching impedance network. The prematching impedance network is coupled to the selected power amplifier controlled by the dynamic bias controller. When the selected power amplifier is activated (turned on) by the dynamic bias controller, the prematching impedance network adjusts the system impedance to a desired value. When the selected power amplifier is deactivated (turned off) by the dynamic bias controller, the prematching impedance network adjusts the system impedance to another desired value. The prematching impedance network may be coupled to the input or the output of the selected power amplifier. Alternatively, two prematching impedance networks could be employed, one connected to the input and the other connected to the output of the selected power amplifier. Furthermore, the prematching impedance network may be further controlled by the dynamic bias controller such that switches couple and decouple the prematching impedance network from the mobile communication device circuitry.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.